Sets of labeled energy transfer fluorescent primers and their use in multi component analysis

ABSTRACT

Sets of fluorescent energy transfer labels and methods for their use in multi component analysis, particularly nucleic acid enzymatic sequencing, are provided. In the subject sets, at least two of the labels are energy transfer labels comprising a common donor and acceptor fluorophore in energy transfer relationship separated by different distances and capable of providing distinguishable fluorescence emission patterns upon excitation at a common wavelength. The subject labels find particular use in a variety of multi-component analysis applications, such as probes in FISH and multi array analyses, as well as primers in nucleic acid enzymatic sequencing applications.

INTRODUCTION

1. Technical Field

The field of this invention is fluorescent labels, particularlyfluorescently labeled primers for use in DNA sequencing applications.

2. Background of the Invention

Fluorescent labels find use in variety of different biological,chemical, medical and biotechnological applications. One example ofwhere such labels find use is in polynucleotide sequencing, particularlyin automated DNA sequencing, which is becoming of critical importance tolarge scale DNA sequencing projects, such as the Human Genome Project.

In methods of automated DNA sequencing, differently sized fluorescentlylabeled DNA fragments which terminate at each base in the sequence areenzymatically produced using the DNA to be sequenced as a template. Eachgroup of fragments corresponding to termination at one of the fourlabeled bases are labeled with the same label. Thus, those fragmentsterminating in A are labeled with a first label, while those terminatingin G, C and T are labeled with second, third and fourth labelsrespectively. The labeled fragments are then separated by size in anelectrophoretic medium and an electropherogram is generated, from whichthe DNA sequence is determined.

As methods of automated DNA sequencing have become more advanced, ofincreasing interest is the use of sets of fluorescent labels in whichall of the labels are excited at a common wavelength and yet emit one offour different detectable signals, one for each of the four differentbases. Such labels provide for a number of advantages, including highfluorescence signals and the ability to electrophoretically separate allof the labeled fragments in a single lane of an electrophoretic mediumwhich avoids problems associated with lane to lane mobility variation.

Although such sets of labels have been developed for use in automatedDNA sequencing applications, heretofore the differently labeled membersof such sets have each emitted at a different wavelength. Thus,conventional automated detection devices currently employed in methodsin which all of the enzymatically produced fragments or primer extensionproducts are separated in the same lane must be able to detect emittedfluorescent light at four different wavelengths. This requirement canprove to be an undesirable limitation. More specifically, carrying outsequencing on vast numbers of different DNA templates simultaneouslyincreases the number of different fragments and corresponding labelsrequired. At the same time, there is a need for a reduction in thecomplexity of the detection device, e.g. a device which can operate withlight detection at only two wavelengths is preferable.

It would therefore be desirable to develop sets of fluorescent labelscapable of providing four distinguishable signals, where the number ofwavelengths associated with the four different signals is less than thenumber of different labels, e.g. where four different labels providesignals comprising emitted light at from one to two wavelengths. Withsuch sets one could either: (1) reduce the complexity of automateddetector devices or (2) increase the throughput of detectors capable ofdetecting at four different wavelengths, thereby achieving sequencingtwo DNA templates, or the same double stranded templates from both the5' and 3' end, simultaneously.

Relevant Literature

DNA sequencing is reviewed in Griffin & Griffin, Appl. Biochem.Biotechnol. (1993) 38:147-159. Fluorescence energy transfer labels andtheir use in DNA sequencing applications are described in Ju et al.,Nucleic Acids Res. (1996) 24:1144-1148; Ju et al., Nat. Med. (1996)2:246-249; Ju et al., Anal. Biochem. (1995) 231:131-140; Ju et al.,Proc. Natl. Acad. Sci. USA (1995) 92:4347-4351. Use of fluorescentenergy transfer labels for non-DNA sequencing multi component analysisapplication is described in Wang et al., Anal. Chem. (1995)67:1197-1203; Ziegle et al., Genomics (1992) 14:1026-1031; and Repp etal., Leukemia (1995) 9:210-215. Other references describingmulti-component analysis applications include Schena et al., Science(1995) 270:467-469.

Other references of interest include U.S. Pat. Nos. 4,996,143 and5,326,692, as well as Glazer and Streyer, Biophys. J. (1983) 43:383-386,Huang et al., Anal. Chem. (1992) 64:2149-2154; Prober et al., Science(1987) 336-341; Smith et al., Nature (1986) 321:674-679, Lu et al, J.Chromat. A (1994) 680:497-501 and Ansorge et al., Nucleic Acids Res.(1987) 15:4593-4603.

SUMMARY OF THE INVENTION

Sets of fluorescent labels, particularly labeled primers, as well asmethods for their use in multi component analysis, are provided. Atleast two of the labels of the subject sets comprise a common donor andacceptor fluorescer component in energy transfer relationship separatedby different distances, such that the labels provide distinguishablefluorescent signals upon excitation at a common light wavelength. Thesubject sets of labels find use in a variety of applications requiring aplurality of distinguishable fluorescent labels, and find particular useas primers in nucleic acid enzymatic sequencing applications. Primerswith the same labels which produce distinguishable emission patterns canbe produced because energy transfer between the acceptor and donorfluorphores is a function of the separation distance between theacceptor and donor in the label. By changing the distance, differentfluorescence emission patterns are obtained.

BRIEF DESCRIPTION OF THE FIGURES

The file of this patent contains at least one drawing executed in color.Copies of this patent with color drawing(s) will be provided by thePatent and Trademark Office upon request and payment of the necessaryfee.

FIG. 1 shows the general labeling concept using four fluorescentmolecules to generate at least eight fluorescent dye-labeled primerswith distinguishable fluorescence emission patterns.

FIG. 2 shows the structure of the four primers labeled with twodifferent fluorescent dyes, 6-carboxyfluoroscein (FAM, F) as a donor and6-carboxyrhodamine (ROX, R) as an acceptor. The numbers in the primername indicate the intervening nucleotides between the donor andacceptor.

FIG. 3 shows that the fluorescence signal of the four fluorescentprimers is sufficiently different to code for four nucleotides T (F6R),G (F13R), A (F16R), C (F16F). It also shows that the primer F16T using6-carboxy tetramethyl rhodamine (TAMRA, T) to replace ROX (R) as anacceptor displays almost equal fluorescence signal intensity of F (blue)and T (black). The fluorescence signals shown are the electropherogramsof the single base extension fragments from each primer obtained in theABI four color fluorescent 377 DNA sequencer which has the appropriatefilters to detect fluorescence signals from FAM (Fλ_(em)(max) =525 nm),ROX (Rλ_(em)(max) =605 nm) and TAMRA (Tλ_(em)(max) =580 nm).

FIG. 4 shows that the fluorescence intensity of the single baseextension fragments from primer F6R (T fragments) and F13R (G fragments)due to energy transfer from F to R is much higher than that of thesingle base fragments generated with primer R15R (T fragments) whichcarries two ROX dyes but with same sequence as F6R and F13R. Sameconcentration of the primer and other sequencing reagents were used inthe comparison.

FIG. 5 shows a small portion of the raw sequencing data in 2-color mode(FAM, Fλ_(em)(max) =525 nm, blue; ROX, Rλ_(em)(max) =605 nm, red)generated by primer F6R (T), F13R (G), F16R (A), F16F (C) and a cDNAclone which has a polyA tail at the 3' end. Sequences can be called bythe color patterns of each peak.

FIGS. 6A to 6B shows a large portion of the raw sequencing data (fromnucleotide 30 to 130) in 2-color mode (FAM, Fλ_(em)(max) =525 nm, blue;ROX, Rλ_(em)(max) =605 nm, red) generated by primer F6R (T), F13R (G),F16R (A), F16F (C) and a cDNA clone which has a polyA tail at the 3'end. Sequences can be called by the color patterns of each peak. Sampleswere prepared using Thermo Sequenase Kit (Amersham LIFE SCIENCE) and runon a ABI 377 DNA sequencer with virtual filter A that detects thefluorescence signal from FAM and ROX.

FIG. 7 is a shematic of the Sanger enzymatic DNA sequencing method.

DEFINITIONS

The term "fluorescent label" refers to a compound comprising at leastone fluorophore bonded to a polymer.

The term "energy transfer fluorescent label" refers to a compoundcomprising at least two fluorophores in energy transfer relationship,where the fluorophores are bonded to a spacer component, e.g. apolymeric moiety, which separates the two fluorphores by a certaindistance.

The term "enzymatic sequencing," "Sanger Method," "dideoxy technique,"and "chain terminator technique," are used interchangeably herein todescribe a method of sequencing DNA named after its main developer, F.Sanger. The technique uses a single-stranded DNA template, a short DNAprimer and a polymerase enzyme to synthesize a complementary DNA strand.The primer is first annealed to the single-stranded template and thereaction mixture is then split into four aliquots and deoxynucleosidetriphosphates (dNTPs) plus a dideoxynucleoside triphosphate (ddNTP) areadded such that each tube has a different ddNTP. The polymerase willincorporate a ddNTP opposite its complementary base on the template butno further dNTPs can be added as the ddNTP lacks a 3' hydroxyl group.The ratio of ddNTP to dNTP is such that the polymerase will terminatethe growing DNA chain at all positions at which the ddNTP can beinserted and so a nested set of fragments (i.e. primer extensionproducts) is formed which all have one end, the primer, in common. Thefragments are labeled so that when the four reaction mixtures areelectrophoresed through a polyacrylamide gel, a gel band pattern orladder is formed from which the DNA sequence can be read directly. Theprocess is shown schematically in FIG. 7.

The term "enzymatically produced" means produced at least in part as aresult of an action of an enzyme, e.g. fragments of nucleotides areproduced when an enzyme catalyzes a reaction whereby a larger sequencesis cleaved into two or more fragments.

The term "primer" shall mean a polymer sequence which is complementaryand capable of hybridizing to some part of a single stranded nucleotidesequence being sequenced which primer is used to initiate DNA synthesisin vitro.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Sets of fluorescent labels, particularly sets of fluorescently labeledprimers, and methods for their use in multi component analysisapplications, particularly nucleic acid enzymatic sequencingapplications, are provided. At least two of the label members of the setare energy transfer labels having a common donor and acceptorfluorophore separated by sufficiently different distances so that thetwo labels provide distinguishable fluorescent signals upon excitationat a common wavelength. In further describing the subject invention, thesubject sets will first be described in greater detail followed by adiscussion of methods for their use in multi component analysisapplications.

Before the subject invention is further described, it is to beunderstood that the invention is not limited to the particularembodiments of the invention described below, as variations of theparticular embodiments may be made and still fall within the scope ofthe appended claims. It is also to be understood that the terminologyemployed is for the purpose of describing particular embodiments, and isnot intended to be limiting. Instead, the scope of the present inventionwill be established by the appended claims.

It must be noted that as used in this specification and the appendedclaims, the singular forms "a," "an" and "the" include plural referenceunless the context clearly dictates otherwise. Unless defined otherwiseall technical and scientific terms used herein have the same meaning ascommonly understood to one of ordinary skill in the art to which thisinvention belongs.

The subject sets of fluorescent labels comprise a plurality of differenttypes of labels, wherein each type of label in a given set is capable ofproducing a distinguishable fluorescent signal from that of the othertypes of labels in different sets. Labels in the different sets generatedifferent signals, preferably, though not necessarily upon excitation ata common excitation wavelength. For DNA sequencing applications, thesubject sets will comprise at least 2 different types of labels, and maycomprise 8 or more different types of labels, where for manyapplications the number of different types of labels in the set will notexceed 6, and will usually not exceed four, where at least two of thedifferent types of labels are energy transfer labels sharing a commondonor and acceptor fluorescer, as described in greater detail below. Forother applications, such as fluorescence in situ hybridization (FISH),substantially more than 8 labels are ideal so that multiple targets canbe analyzed.

The distinguishable signals generated by the "at least two energytransfer labels" will at least comprise the intensity of emitted lightat one to two wavelengths. Preferably, the distinguishable signalsproduced by the "at least two energy transfer labels" will comprisedistinguishable fluorescence emission patterns, which patterns aregenerated by plotting the intensity of emitted light from differentlysized fragments at two wavelengths with respect to time as differentlylabeled fragments move relative to a detector, which patterns are knownin the art as electropherograms. For analyses not based onelectrophoresis, such as micro-array chip based assays, differenttargets tagged with a specific label can be differentiated from eachother by the unique fluorescence patterns. For example, in one type oflabel of a set the intensity of emitted light at a first wavelength maybe twice that of the intensity of emitted light at a second wavelengthand in the second label the magnitude of the intensities of lightemitted at the two wavelengths may be reversed, or light may be emittedat only one intensity. The different patterns are generated by varyingthe distance between the donor and acceptor. These patterns emitted fromeach of these labels are thus distinguishable.

The subject sets will comprise a plurality of different types offluorescent labels, where at least two of the labels and usually all ofthe labels are energy transfer labels which comprise at least oneacceptor fluorophore and at least one donor fluorophore in energytransfer relationship, where such labels may have more complexconfigurations, such as multiple donors and/or multiple acceptors, e.g.donor 1, acceptor 1 and acceptor 2. Critical to the subject sets is thatat least two of the labels of the sets have common donor and accceptorfluorophores, where the only difference between the labels is thedistance between these common acceptor and donor fluorophores. Thus, forsets of labels in which each label comprises a single donor and a singleacceptor, at least one of the energy transfer labels will have a donorfluorophore and acceptor fluorophore in energy transfer relationshipseparated by a distance x and at least one of the energy transfer labelswill comprise the same donor and acceptor fluorophores in energytransfer relationship separated by a different distance y, where thedistances x and y are sufficiently different to provide fordistinguishable fluorescence emission patterns upon excitation at acommon wavelength, as described above. In those sets comprising a thirdlabel having the same donor and acceptor fluorophores as the first andsecond label, the distance z between the donor and acceptor fluorophorewill be sufficiently different from x and y to ensure that the thirdlabel is capable of providing a distinguishable fluorescence emissionpattern from the first and second labels. Thus, in a particular set oflabels, one may have a plurality of labels having the same donor andacceptor fluorophores, where the only difference among the labels is thedistance between the donor and acceptor fluorophores. To ensure thatdifferent types of labels of a set having common donor and acceptorfluorophores yield distinguishable fluorescence emission patterns, thedistances between the donor and acceptor fluorophores will differ by atleast about 5%, usually by at least about 10% and more usually by atleast about 20% and will generally range from about from about 4 to 200Å, usually from about 12 to 100 Å and more usually from about 15 to 80Å, where the minimums in such distances are determined based oncurrently available detection devices and may be reduced as detectiontechnology becomes more sensitive, therefore more distinct labels can begenerated.

In one preffered embodiment, at least a portion of, up to and includingall of, the labels of the subject sets will comprise a donor andacceptor fluorescer component in energy transfer relationship andcovalently bonded to a spacer component, i.e. energy transfer labels.Thus, one could have a set of a plurality of labels in which only two ofthe labels comprise the above mentioned donor and acceptor fluorescercomponents and the remainder of the labels comprise a single fluorescercomponent. Preferably, however, all of the labels will comprise a donorand acceptor fluorescer component. Generally, for one donor and oneacceptor ET systems, if a set comprises n types of energy transferlabels, the number of different types of acceptor fluorophores presentin the energy transfer labels of the set will not exceed n-1. Thus, ifthe number of different types of energy transfer labels in the set isfour, the number of different acceptor fluorophores in the set will notexceed 3, and will usually not exceed 2.

In other preferred embodiments, additional combinations of labels arepossible. Thus, in a set of labels, two of the labels could be energytransfer labels sharing common donor and acceptor fluorophores separatedby different distances and the remaining labels could be additionalenergy transfer labels with different donor and/or acceptorfluorophores, non-energy transfer fluorescent labels, and the like.

In the energy transfer labels of the subject sets, the spacer componentto which the fluorescer components are covalently bound will typicallybe a polymeric chain or other chemical moiety capable of acting as aspacer for the donor and acceptor fluorophore components, such as arigid chemical moiety, such as chemicals with cyclic ring or chainstructures which can separate the donor and acceptor and which also canbe incorporated with an active group for attaching to the targets to beanalyzed, where the spacer component will generally be a polymericchain, where the fluorescer components are covalently bonded throughlinking groups to monomeric units of the chain, where these monomericunits of the chain are separated by a plurality of monomeric unitssufficient so that energy transfer can occur from the donor to acceptorfluorescer components. The polymeric chains will generally be eitherpolynucleotides, analogues or mimetics thereof; or peptides, peptideanalogues or mimetics thereof, e.g. peptoids. For polynucleotides,polynucleotide analogues or mimetics thereof, the polymeric chain willgenerally comprise sugar moieties which may or may not be covalentlybonded to a heterocyclic nitrogenous base, e.g. adenine, guanine,cytosine, thymine, uracil etc., and are linked by a linking group. Thesugar moieties will generally be five membered rings, e.g. ribose, orsix membered rings, e.g. hexose, with five membered rings such as ribosebeing preferred. A number of different sugar linking groups may beemployed, where illustrative linking groups include phosphodiester,phosphorothioate, methylene(methyl imino)(MMI), methophosphonate,phosphoramadite, guanidine, and the like. See Matteucci & Wagner, Nature(1996) Supp 84:20-22. Peptide, peptide analogues and mimetics thereofsuitable for use as the polymeric spacer include peptoids as describedin WO 91/19735, the disclosure of which is herein incorporated byreference, where the individual monomeric units which are joined throughamide bonds may or may not be bonded to a heterocyclic nitrogenous base,e.g., peptide nucleic acids. See Matteucci & Wagner supra. Generally,the polymeric spacer components of the subject labels will be peptidenucleic acid, polysugarphosphate as found in energy transfer cassettesas described in PCT/US96/13134, the disclosure of which is hereinincorporated by reference, and polynucleotides as described inPCT/US95/01205, the disclosure of which is herein incorporated byreference.

Both the donor and acceptor fluorescer components of the subject labelswill be covalently bonded to the spacer component, e.g. the polymericspacer chain, through a linking group. The linking group can be variedwidely and is not critical to this invention. The linking groups may bealiphatic, alicyclic, aromatic or heterocyclic, or combinations thereof.Functionalities or heteroatoms which may be present in the linking groupinclude oxygen, nitrogen, sulfur, or the like, where the heteroatomfunctionality which may be present is oxy, oxo, thio, thiono, amino,amido and the like. Any of a variety of the linking groups may beemployed which do not interfere with the energy transfer and gelelectrophoresis, which may include purines or pyrimidines, particularlyuridine, thymidine, cytosine, where substitution will be at an annularmember, particularly carbon, or a side chain, e.g. methyl in thymidine.The donor and/or fluorescer component may be bonded directly to a baseor through a linking group of from 1 to 6, more usually from 1 to 3atoms, particularly carbon atoms. The linking group may be saturated orunsaturated, usually having not more than about one site of aliphaticunsaturation.

Though not absolutely necessarily, generally for DNA sequencingapplications at least one of the donor and acceptor fluorescercomponents will be linked to a terminus of the polymeric spacer chain,where usually the donor fluorescer component will be bonded to theterminus of the chain, and the acceptor fluorescer component bonded to amonomeric unit internal to the chain. For labels comprisingpolyncucleotides, analogues or mimetics thereof as the polymeric chain,the donor fluorescer component will generally be at the 5' terminus ofthe polymeric chain and the acceptor fluorescer component will be bondedto the polymeric chain at a position 3' position to the 5' terminus ofthe chain. For other applications, such as FISH, a variety of labelingapproaches are possible.

The donor fluorescer components will generally be compounds which absorbin the range of about 300 to 900 nm, usually in the range of about 350to 800 nm, and are capable of transferring energy to the acceptorfluorescer component. The donor component will have a strong molarabsorbance co-efficient at the desired excitation wavelength, desirablygreater than about 10⁴, preferably greater than about 10⁵ cm⁻¹ M⁻¹. Themolecular weight of the donor component will usually be less than about2.0 kD, more usually less than about 1.5 kD. A variety of compounds maybe employed as donor fluorescer components, including fluorescein,phycoerythrin, BODIPY, DAPI, Indo-1, coumarin, dansyl, cyanine dyes, andthe like. Specific donor compounds of interest include fluoroscein,rhodamine, cyanine dyes and the like.

Although the donor and acceptor fluorescer component may be the same,e.g. both may be FAM, where they are different the acceptor fluorescermoiety will generally absorb light at a wavelength which is usually atleast 10 nm higher, more usually at least 20 nm or higher, than themaximum absorbance wavelength of the donor, and will have a fluorescenceemission maximum at a wavelength ranging from about 400 to 900 nm. Aswith the donor component, the acceptor fluorescer component will have amolecular weight of less than about 2.0 kD, usually less than about 1.5kD. Acceptor fluorescer moieties may be rhodamines, fluorosceinderivatives, BODIPY and cyanine dyes and the like. Specific acceptorfluorescer moieties include FAM, JOE, TAM, ROX, BODIPY and cyanine dyes.

The distance between the donor and acceptor fluorescer components willbe chosen to provide for energy transfer from the donor to acceptorfluorescer, where the efficiency of energy transfer will be from 20 to100%. Depending on the donor and acceptor fluorescer components, thedistance between the two will generally range from 4 to 200 Å, usuallyfrom 12 to 100 Å and more usually from 15 to 80 Å, as described above.

For the most part the labels of the subject sets will be described bythe following formula: ##STR1## wherein: D is the donor fluorescercomponent, which may consist of more than two different donors separatedby a spacer;

N is the spacer component, which may be a polymeric chain or rigidchemical moiety, where when N is a polymeric spacer that comprisesnucleotides, analogues or mimetics thereof, the number of monomericunits in N will generally range from about 1 to 50, usually from about 4to 20 and more usually from about 4 to 16;

A is the acceptor fluorescer component, which may consist of more thantwo different acceptors separated by a spacer; and

X is optional and is generally present when the labels are incorporatedinto oligonucleotide primers, where X is a functionality, e.g. anactivated phosphate group, for linking to a mono- or polynucleotide,analogue or mimetic thereof, particularly a deoxyribonucleotide,generally of from 1 to 50, more usually from 1 to 25 nucleotides.

For sets to be employed in nucleic acid enzymatic sequencing in whichthe labels are to be employed as primers, the labels of the subject setswill comprise either the donor and acceptor fluorescer componentsattached directly to a hybridizing polymeric backbone, e.g. apolynucleotide, peptide nucleic acid and the like, or the donor andacceptor fluorescer components will be present in an energy transfercassette attached to a hybridizable component, where the energy transfercassette comprises the fluorescer components attached to anon-hybridizing polymeric backbone, e.g. a universal spacer. SeePCT/US96/13134 and Ju et al., Nat. Med. (1996) supra, the disclosures ofwhich are herein incorporated by reference. The hybridizable componentwill typically comprise from about 8 to 40, more usually from about 8 to25 nucleotides, where the hybridizable component will generally becomplementary to various commercially available vector sequences suchthat during use, synthesis proceeds from the vector into the clonedsequence. The vectors may include single-stranded filamentousbacteriophage vectors, the bacteriophage lambda vector, pUC vectors,pGEM vectors, or the like. Conveniently, the primer may be derived froma universal primer, such as pUC/M13, λgt10, λgt11, and the like, (SeeSambrook et al., Molecular Cloning: A Laboratory Manual, 2nd ed., CSHL,1989, Section 13), where the universal primer will have been modified asdescribed above, e.g. by either directly attaching the donor andacceptor fluorescer components to bases of the primer or by attaching anenergy transfer cassette comprising the fluorescer components to theprimer.

Sets of preferred energy transfer labels comprising donor and acceptorfluorescers covalently attached to a polynucleotide backbone in theabove D-N-A format include: (1) F6R, F13R, F16R and F16F; wheredifferent formats can employed as long as the four primers displaydistinct fluorescence emission patterns.

The fluorescent labels of the subject sets can be readily synthesizedaccording to known methods, where the subject labels will generally besynthesized by oligomerizing monomeric units of the polymeric chain ofthe label, where certain of the monomeric units will be covalentlyattached to a fluorescer component.

The subject sets of fluorescent labels find use in applications where atleast two components of a sample or mixture of components are to bedistinguishably detected. In such applications, the set will be combinedwith the sample comprising the to be detected components underconditions in which at least two of the components of the sample ifpresent at all will be labeled with first and second labels of the set,where the first and second labels of the set comprise the same donor andacceptor fluorescer components which are separated by differentdistances. Thus, a first component of the sample is labeled with a firstlabel of the set comprising donor and acceptor fluorescer componentsseparated by a first distance X. A second component of the sample islabeled with a second label comprising the same donor and fluorescercomponents separated by a second distance Y, where X and Y are asdescribed above. The labeled first and second components, which may ormay not have been separated from the remaining components of the sample,are then irradiated by light at a wavelength capable of a being absorbedby the donor fluorescer components, generally at a wavelength which ismaximally absorbed by the donor fluorescer components. Irradiation ofthe labeled components results in the generation of distinguishablefluorescence emission patterns from the labeled components, a firstfluorescence emission pattern generated by the first label and secondpattern being attributable to the second label. The distinguishablefluorescence emission patterns are then detected. Applications in whichthe subject labels find use include a variety of multicomponent analysisapplications in which fluorescent labels are employed, including FISH,micro-array chip based assays where the labels may be used as probeswhich specifically bind to target components, DNA sequencing where thelabels may be present as primers, and the like.

The subject sets of labels find particular use in polynucleotideenzymatic sequencing applications, where four different sets ofdifferently sized polynucleotide fragments terminating at a differentbase are generated (with the members of each set terminating at the samebase) and one wishes to distinguish the sets of fragments from eachother. In such applications, the sets will generally comprise fourdifferent labels which are capable of acting as primers for enzymaticextension, where at least two of the labels will be energy transferlabels comprising differently spaced common donor and acceptorfluorescer components that are capable of generating distinguishablefluorescence emission patterns upon excitation at a common wavelength oflight. Using methods known in the art, a first set of primer extensionproducts all ending in A will be generated by using a first of thelabels of the set as a primer. Second, third and fourth sets of primerextension products terminating in G, C and T will be also beenzymatically produced. The four different sets of primer extensionproducts will then be combined and size separated, usually in anelectrophoretic medium. The separated fragments will then be movedrelative to a detector (where usually either the fragments or thedetector will be stationary). The intensity of emitted light from eachlabeled fragment as it passes relative to the detector will be plottedas a function of time, i.e. an electropherogram will be produced. Since,the labels of the subject sets will generally emit light in only twowavelengths, the plotted electropherogram will comprise light emitted intwo wavelengths. Each peak in the electropherogram will correspond to aparticular type of primer extension product (i.e. A, G, C or T), whereeach peak will comprise one of four different fluorescence emissionpatterns. To determine the DNA sequence, the electropherogram will beread, with each different fluorescence emission pattern related to oneof the four different bases in the DNA chain.

Where desired, two sets of labels according to the subject invention maybe employed, where the distinguishable fluorescence emission patternsproduced by the labels in the first set will comprise emissions at afirst and second wavelength and the patterns produced by the second setof labels will comprise emissions at a third and fourth wavelength. Byusing two such sets in conjunction with one another, one could detectprimer extension products produced from two different template DNAstrands at essentially the same time in a conventional four colordetector, thereby doubling the throughput of the detector.

The subject sets of labels may be sold in kits, where the kits may ormay not comprise additional reagents or components necessary for theparticular application in which the label set is to be employed. Thus,for sequencing applications, the subject sets may be sold in a kit whichfurther comprises one or more of the additional requisite sequencingreagents, such as polymerase, nucleotides, dideoxynucleotides and thelike.

The following examples are offered by way of illustration and not by wayof limitation. The following examples are put forth so as to providethose of ordinary skill in the art with a complete disclosure anddescription of how to make and use the subject sets of fluorescentlabels.

EXPERIMENTAL

A. Design and synthesis of the fluorescent primers.

An example of a general labeling scheme using the energy transferconcept to generate at least eight fluorescent primers from fourfluorescent dyes is described in FIG. 1. To demonstrate the practicalityof the labeling approach, two fluorescent dyes 6-carboxyfluorescein(FAM, Fλ_(em)(max) =525 nm) as a donor and 6-carboxy-X-rhodamine (ROX,Rλ_(em)(max) =605 nm, red) as an acceptor are chosen to generate fourfluorescent oligonucleotide primers, which are subsequently used for DNAsequencing on a cDNA clone. The structures of the fluorescent primersare presented in FIG. 2. Oligodeoxynucleotides (25-bases long) with thesequence 5'-TTTTTTTTTTTTTTTTTTTTTTTAC-3' (SEQ ID NO:01)were synthesizedwith donor-acceptor fluorophore pairs separated by different distances.The 25-mer contains a modified base introduced by the use of5'-dimethoxytrityl-5- N-(trifluoroacetylaminohexyl)-3-acrylimido!-2'-deoxyuridine, 3'-(2-cyano-ethyl)-(N,N-diisopropyl)!-phosphoramidite (Amino-Modifier C6dT, Glen Research, Sterling, Va.) which has a protected primary aminelinker arm. The donor dye was attached to the 5' end of the oligomer,and the acceptor dye was attached to the primary amine group on themodified base. The primers are synthesized and purified according to thepublished procedure (Ju, J., Ruan, C., Fuller, C. W. Glazer, A. N. andMathies, R. A. (1995) Proc. Natl. Acad. Sci. USA 92, 4347-4351). The ETprimers are named using the abbreviation D-N-A, where D is the donor, Ais the acceptor, and N is the number of intervening nucleotides betweenD and A. In all the primers prepared, 6-carboxyfluorescein (FAM, F, withfluorescence emission maximum at 525 nm) is selected as a common donor,and 6-carboxy-X-rhodamine (ROX, R, with fluorescence emission maximum at605 nm) is selected as an acceptor, except in one example whereN,N,N',N'-tetramethyl-6-carboxyrhodamine (TAMRA, T, with fluorescenceemission maximum at 580 nm) is chosen as an acceptor as shown in FIG. 3.

Five fluorescent primers with their unique fluorescence signal patternsare shown in FIG. 3. For primer F6R, the energy transfer efficiency fromdonor F to R is higher than 90%, therefore it only displays a dominantred color from acceptor R. For primer F13R, the ET efficiency is lessthan that in F6R, therefore F13R not only displays a high red signalfrom the acceptor R and also a blue signal from F with intensityapproximately 40% of the red signal. For primer F16R, the ET efficiencyis even less than that in F13R, which results in an approximately equalsignal intensity from R (red) and F (blue). For primer F16F carrying twoFAM molecules, the fluorescence signal is dominated by blue. For primerF16T that uses TAMRA (T) as an acceptor, the fluorescence signal from F(blue) is almost in equal intensity as T (Black). It is clear from theseexamples that at least five different fluorescent labels are generatedusing only three dyes. With two dyes FAM and ROX, four fluorescentprimers are generated that have sufficiently different fluorescencesignals to code for the for DNA sqeuencing fragments ended withnucleotides T (F6R), G (F13R, A (F16R) and C (F16F). These four primersare then chosen for evaluation in DNA sequencing using a cDNA clone witha polyA tail which can be primed by the designed primers.

B. DNA Sequencing procedure.

Sequencing was performed using a cDNA clone labeled Incyte clone 1 shownbelow and Thermo Sequenase sequencing kit (Amersham Life Science) on anABI 377 sequencer.

INCYTE CLONE 1 (The italic sequence is the one shown in FIG. 6.)##STR2##

Four reactions were run, one for each dye/ddNTP combination with 0.2pmole of the appropriate primer. The reactions containing ddCTP were runwith the F16F primer, ddATP with the F16R primer, ddGTP with the F13R,and ddTTP with the F6R primer. Fifteen cycles of 94° C. for 20 seconds,47° C. for 40 seconds and 68° C. for 60 seconds were carried out for thesequencing reaction mixture and then cooled to 4° C. The four reactionmixtures for each sequence were then combined into one vial and 50 μl of100% ethanol were added to precipitate the DNA fragments. The DNA wasprecipitated by centrifugation for 30 min at 4° C. and then washed oncewith 70% ethanol. The precipitated DNA was vacuum dried, and resuspendedin 4 μl of deionized formamide containing 8.3 mM EDTA and heated at 95°C. for 2 min. The denatured DNA was loaded on a 4% polyacrylamide 7Murea denaturing gel mounted in the instrument. Electrophoresis wasconducted for 3.5 hours using 1X Tris-borate-EDTA buffer.

C. DNA sequencing results with the four fluorescent primers.

FIG. 4 shows that the fluorescence intensity of the single baseextension fragments from primer F6R (T fragments) and F13R (G fragments)due to energy transfer from F to R is much higher than that of thesingle base fragments generated with primer R15R (T fragments) whichcarries two ROX dyes but with same sequence as F6R and F13R. The sameconcentration of the primer and other sequencing reagents were used inthe comparison. A small portion of the DNA sequencing raw data in a twocolor mode sampled from FAM and ROX using primer F6R, F13R, F16R andF16F on an ABI 377 DNA sequencer is shown in FIG. 5. From this raw data,sequences can be determined by the color ratio of the peak in theelectropherograms. FIG. 6 shows a large portion of the raw sequencingdata (from nucleotide 30 to 130) in 2-color mode generated by primer F6R(T), F13R (G), F16R (A), F16F (C) and a cDNA clone which has a polyAtail at the 3' end. Sequences can be called by the color patterns ofeach peak without applying any mobility shift correction on the rawdata. For example, when the blue and red signals under one peak havealmost the same intensity, the peak is assigned as an A; when only adominant blue signal is seen in a peak, it was assigned as a C; when redsignal is slightly higher than the blue signal in a peak, it wasassigned as a G; when the red signal is much higher than the blue signalin a peak, it was assigned as a T.

It is clear from the experimental data that with two fluorescent dyes,using energy transfer concepts which offer higher fluorescence signals,four fluorescent primers can be generated with sufficiently differentfluorescence signal patterns for sequencing DNA successfully. With twoadditional different fluorescent molecules, using the same principlepresented, another four fluorescent primers can be constructed. Thus,with a DNA sequencer equipped with the appropriate 4-color filters, twosets of DNA sequencing samples can be analyzed simultaneously, doublingthe sequencing throughput. These sets of unique fluorescent labelsconstructed with the concepts presented will find wide applications inother multiple component analysis projects.

It is evident from the above results and discussion that the sets of alabels of the subject invention provide for a number of advantages. Forexample, where the sets of labels are employed in DNA sequencing, onecan employ a detector capable of detecting at only two very wellseparated wavelengths. Therefore, the detector can sample a largeportion of the fluorescence signals, providing higher sensitivity fordetection and increasing readlength of the sequence. Alternatively, withconventional detectors comprising four different wavelength detectors,one can effectively double the throughput obtainable with thesedetectors by sequencing two different strands with two sets of labelsaccording to the subject invention. Thus, the subject sets of labelsrepresent a significant contribution to the art.

All publications and patent applications cited in this specification areherein incorporated by reference as if each individual publication orpatent application were specifically and individually indicated to beincorporated by reference. The citation of any publication is for itsdisclosure prior to the filing date and should not be construed as anadmission that the present invention is not entitled to antedate suchpublication by virtue of prior invention.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it is readily apparent to those of ordinary skill in theart in light of the teachings of this invention that certain changes andmodifications may be made thereto without departing from the spirit orscope of the appended claims.

What is claimed is:
 1. A set of at least 2 different fluorescent labels,said set comprising:a first energy transfer fluorescent label comprisingat least one donor fluorophore and at least one acceptor fluorophore inenergy transfer relationship separated by a distance x; and a secondenergy transfer fluorescent label comprising said at least one donorfluorophore and said at least one acceptor fluorophore in energytransfer relationship separated by a distance y; wherein: (a) said donorfluorophores of said first and second labels are the same; (b) saidacceptor fluorophores of said first and second labels are the same; and(c) x and y are sufficiently different so that said first and secondfluorescent labels provide distinguishable fluorescent signals whereinall of the labels of said set are acceptor fluorophores are selectedfrom the group consisting of TAM, JOE, FAM, ROX, BODIPY, fluoresein andcyanine dyes.
 2. The set according to claim 1, wherein said set furthercomprises at least one non-energy transfer fluorescent label.
 3. The setaccording to claim 1, wherein said set comprises n distinct energytransfer labels, wherein the total number of different acceptorfluorophores among said n distinct energy transfer labels does notexceed n-1.
 4. The set according to claim 1, wherein said donor andacceptor fluorophores of said energy transfer labels are bonded to apolynucleotide.
 5. The set according to claim 1, wherein said donor andacceptor fluorophores of said energy transfer labels are bonded to aspacer selected from the group consisting of a peptide nucleic acid anda peptide.
 6. The set according to claim 1, wherein said energy transferlabels comprise an energy transfer cassette.
 7. The set according toclaim 1, wherein all of the labels of said set are excited at a commonwavelength and said acceptor fluorophores are selected from the groupconsisting of TAM, JOE, FAM, BODIPY, fluorescein and cyanine dyes. 8.The set according to claim 3, wherein n is
 4. 9. The set according toclaim 8, wherein the number of different acceptor fluorophores amongsaid 4 energy transfer labels is
 2. 10. A set of four differentfluorescently labeled energy transfer oligonucleotide primers, said setcomprising:a first energy transfer fluorescently labeled oligonucleotideprimer comprising a donor fluorophore and an acceptor fluorophore inenergy transfer relationship separated by a distance x; a second energytransfer fluorescently labeled oligonucleotide primer comprising saiddonor fluorophore and said acceptor fluorophore in energy transferrelationship separated by a distance y; a third energy transferfluorescently labeled oligonucleotide primer comprising said donorfluorophore and said acceptor fluorophore in energy transferrelationship separated by a distance z; and a fourth energy transferfluorescently labeled oligonucleotide primer wherein said donor andacceptor fluorophores have the same fluorescence emission; wherein: (a)said donor fluorophore of said first, second and third labels are thesame; (b) said acceptor fluorophores of said first, second and thirdlabels are the same and selected from the group consisting of TAM, JOE,FAM, ROX, BODIPY, fluorescein and cyanine dyes; and (c) x, y and z aresufficiently different so that said first through fourth fluorescentlylabeled oligonucleotide primers provide distinguishable fluorescenceemission patterns.
 11. The set according to claim 10, wherein saidfirst, second, third and fourth energy transfer labeled primers comprisea common donor fluorophore.
 12. The set according to claim 10, whereinsaid energy transfer fluorescently labeled primers further compriseenergy transfer cassettes.
 13. The set according to claim 12, whereinsaid donor and acceptor fluorophores are bonded to a polysugarphosphate.
 14. A set of four different energy transfer fluorescentlylabeled oligonucleotide primers for use in enzymatic sequencing, saidset comprising:a first energy transfer fluorescently labeledoligonucleotide comprising a donor fluorophore bonded to the 5' terminusand an acceptor fluorophore bonded to the 7th nucleotide 3' from the 5'terminus; a second energy transfer fluorescently labeled oligonucleotidecomprising said donor fluorophore bonded to the 5' terminus and saidacceptor fluorophore bonded to the 14th nucleotide 3' from the 5'terminus; a third energy transfer fluorescently labeled oligonucleotidecomprising said donor fluorophore bonded to the 5' terminus and saidacceptor fluorophore bonded to the 17th nucleotide 3' from the 5'terminus; and a fourth energy transfer fluorescently labeledoligonucleotide comprising said donor fluorophore bonded to the 5'terminus and said donor fluorophore bonded to the 17th nucleotide 3'from the 5' terminus; wherein (a) said donor fluorophore of said first,second, third and fourth labeled oligonucleotides are the same; and (b)said acceptor fluorophores of said first, second, third and fourthlabeled oligonucleotides are the same and are selected from the groupconsisting of TAM, JOE, FAM, ROX, BODIPY, fluorescein and cyanine dyes.15. The set according to claim 14, wherein said donor fluorophore isFAM.
 16. The set according to claim 14, wherein said acceptorfluorophore is ROX.
 17. A kit for use in DNA sequencing, said kitcomprising:a set of four fluorescently labeled oligonucleotide primers,wherein at least two of said oligonucleotide primers have a common donorand acceptor fluorophore in energy transfer relationship and areseparated by different distances wherein all of the labels of said setare acceptor fluorophores are selected from the group consisting of TAM,JOE, FAM, ROX, BODIPY, fluoresein and cyanine dyes.
 18. The kitaccording to claim 17, wherein said kit further comprises polymerase.19. The kit according to claim 17, wherein said kit further comprisesdeoxynucleotides and dideoxynucleotides.
 20. The kit according to claim17, wherein said common acceptor fluorophore of said at least twooligonucleotide primers is selected from the group consisting of TAM,JOE, FAM, ROX, BODIPY, fluorescein and cyanine dyes.